Types of fat, transportation of fat in the blood, FUnction of fat in the diet, DHA accumulation in the eye, Disc shedding in the retina, DHA conservation in eye, Role of DHA in the eye

1. Unit: III
Lipids and eye
Carbohydrates and eye
Vitamins and eye
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2. Unit: III
Lipids and eye
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3. Lipids
The term ‘lipids’ is applied to a group of naturally occurring substances characterized
by their insolubility in water, greasy, feel and solubility in some organic solvents.
Lipids
Simple Lipids
Compound
Lipids
Phospholipids Glycolipids
Waxes Derived Lipids

4. Lipids
Simple lipids (ex: Triolein)
• Oils and fats: These are esters of fatty acids and glycerol. Oils and liquids at 20oC,
while fats are solids at 20oC
• Contain fatty acids with glycerol
• Fats and oils are triglycerides
• Fatty acids are divided into two
• Saturated and unsaturated fatty acids

5. Properties of fats
Solubility:
• fats are soluble in ethyl ether, petroleum, acetone, hot alcohol and benzene.
• The quality of fat present in food materials is usually determined by extraction with
ethyl ether or petroleum ether.
Iodine value:
• This is a measure of the extent of unsaturated fatty acids present in fats and oils.
• It is defined as the number of grams of Iodine absorbed by 100g of fat.
• Two atoms of Iodine are added to each unsaturated linkage

6. Lipids
Compound Lipids
Lipids contains fatty acid and glycerol
1. Phospholipids (phosphatides): These contain phosphoric acid an a nitrogenous
base in addition to fatty acids and glycerol (e.g: lecithin and cephalin)
2. Glycolipids: Complex lipids containing carbohydrates in combination with fatty
acids and glycerol (e.g., cerebroside).

7. Lipids

8. Lipids
Waxes
• These are esters of fatty acids and long chain aliphatic alcohols.
• They have high molecular weight monohydroxy alcohols
Derived lipids
• are the substances derived from simple and compound lipids by hydrolysis.
• These includes fatty acids, alcohols, monoglycerides and diglycerides, steroids,
terpenes, carotenoids.

9. Types of fat
Nutritionally fat can be divided into
1. Saturated
2. Unsaturated
3. Trans

10. Types of fat : Unsaturated
Unsaturated fats
• liquid at room temperature
• are considered beneficial fats because they can improve blood cholesterol
levels, ease inflammation, stabilize heart rhythms, and play a number of
other beneficial roles.
• Unsaturated fats are predominantly found in foods from plants, such as
vegetable oils, nuts, and seeds.

11. Types of fat : Unsaturated
There are two types of “good” unsaturated fats:
1. Monounsaturated fats are found in high concentrations in:
• Olive, peanut, and canola oils
• Avocados
• Nuts such as almonds, hazelnuts, and pecans
• Seeds such as pumpkin and sesame seeds
2. Polyunsaturated fats are found in high concentrations in
• Sunflower, corn, soybean, and flaxseed oils
• Walnuts, Flax seeds, Fish
• Canola oil – though higher in monounsaturated fat, it’s also a good source of
polyunsaturated fat.

12. Omega-3 fats
Omega-3 fats are a key family of polyunsaturated fats.
There are three main omega-3s:
• Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) come mainly from
fish, so they are sometimes called marine omega-3s.
• Alpha-linolenic acid (ALA), the most common omega-3 fatty acid in most
Western diets, is found in vegetable oils and nuts (especially walnuts), flax seeds
and flaxseed oil, leafy vegetables, and some animal fat, especially in grass-fed
animals.
• The human body generally uses ALA for energy, and conversion into EPA and
DHA is very limited.

13. Docosahexaenoic acid, C22:6 Ω-3
• DHA, C22:6 Ω -3, is found in high concentrations in a few select mammalian
tissues such as the brain synaptosomes, sperm and the retinal ROS.
• The highest body concentrations of DHA is located in the retinal ROS.
• DHA can be synthesised from the EFA linolenic acid (C18:3 Ω -3);
• the retina is limited in the capacity to synthesise from DHA’s precursor EFA.
• The liver plays an essential role in synthesising DHA from its precursor and for
packaging the newly synthesised, or dietary, DHA into lipoproteins for export to
the retina and other tissues.

14. Omega-3 fats
• The strongest evidence for a beneficial effect of omega-3 fats has to do with
heart disease.
• These fats appear to help the heart beat at a steady clip and not veer into a
dangerous or potentially fatal erratic rhythm.
• Omega-3 fats also lower blood pressure and heart rate, improve blood vessel
function, and, at higher doses, lower triglycerides and may ease inflammation,
which plays a role in the development of atherosclerosis.

15. Omega-3 fats
• A 1-gram capsule of omega-3 fats every day for three years were less likely to
have a repeat heart attack, stroke, or die of sudden death than those who took a
placebo.
• Notably, the risk of sudden cardiac death was reduced by about 50 percent
• Results from the Health Professionals Follow-up Study and others show that men
whose diets are rich in EPA and DHA (mainly from fish and seafood) are less likely
to develop advanced prostate cancer than those with low intake of EPA and DHA.

16. Type of fat: Saturated
Saturated fats
• Foods high in saturated fats raise blood cholesterol.
• These foods include high fat diary (cheese, whole milk, cream, butter and ice
cream), fatty fresh and processed meats and the skin and fat of poultry, lard,
palm oil and coconut oil

17. Type of fat : Trans
Trans Fats
• Trans fatty acids - more commonly called trans fats
• made by heating liquid vegetable oils in the presence of hydrogen gas and nickel
catalyst, a process called hydrogenation.
• Partially hydrogenating vegetable oils makes them more stable and less likely to
become rancid.
• This process also converts the oil into a solid, which makes them function as
margarine or shortening.
• Vanaspathi sold in India consists mostly of hydrogenated refined groundnut oil to
which sesame oil (5%) is added.

18. Type of fat : Trans fat
Trans Fats
• Partially hydrogenated oils can withstand repeated heating without breaking
down, making them ideal for frying fast foods.
• For these reasons, partially hydrogenated oils became a mainstay in restaurants
and the food industry – for frying, baked goods, and processed snack foods.
• Partially hydrogenated oil is not the only source of trans fats in our diets.
• Trans fats are also naturally found in beef fat and dairy fat in small amounts.

19. Rancidity in fats
Hydrolytic rancidity
• When fat is hydrolyzed by lipase,
free fatty acids are formed.
• The odors of low molecular
weight fatty acids contribute to
the rancidity
Oxidative rancidity
• The oxidation takes place at the
unsaturated linkage.
• The addition of oxygen to the
unsaturated linkage results in the
formation of peroxide which on
decomposition, yields aldehyde
and ketones having pronounced
off odor

20. Cholesterol
• The biggest influence on blood cholesterol level is the mix of fats and
carbohydrates in your diet—not the amount of cholesterol you eat from food.
• Although it remains important to limit the amount of cholesterol you eat,
especially if you have diabetes, for most people dietary cholesterol is not as
problematic as once believed.
• The body uses cholesterol as the starting point to make estrogen, testosterone,
vitamin D, and other vital compounds.
• Cholesterol in the bloodstream, specifically the bad LDL cholesterol, is what’s
most important in determining health risk.

21. How Fat Moves from Food to the Bloodstream
• Fat and cholesterol can’t dissolve in water or blood.
• Instead, the body packages fat and cholesterol into tiny, protein-covered
particles called lipoproteins.
• Lipoproteins can transport a lot of fat; they mix easily with blood and flow
with it.
• Some of these particles are big and fluffy, while others are small and dense.
• The most important ones are low-density lipoproteins (LDL), high-density
lipoproteins (HDL) , and triglycerides.

22. How Fat Moves from Food to the Bloodstream
Low Density lipoproteins
• Low-density lipoproteins (LDL) carry cholesterol from the liver to the rest of
the body.
• Cells latch onto these particles and extract fat and cholesterol from them via
receptor mediated endocytosis using LDL receptor.
• When there is too much LDL cholesterol in the blood, these particles can form
deposits in the walls of the coronary arteries and other arteries throughout
the body.
• Such deposits, called plaque, can narrow arteries and limit blood flow.
• When plaque breaks apart, it can cause a heart attack or stroke.
• Because of this, LDL cholesterol is often referred to as bad, or harmful,
cholesterol.

23. How Fat Moves from Food to the Bloodstream
High Density lipoproteins
• High-density lipoproteins (HDL) scavenge cholesterol from the bloodstream,
from LDL, and from artery walls and ferry it back to the liver for disposal.
• Think of HDL as the garbage trucks of the bloodstream.
• HDL cholesterol is often referred to as good, or protective, cholesterol.

24. How Fat Moves from Food to the Bloodstream
Triglycerides
• Triglycerides make up most of the fat that you eat and that travels through the
bloodstream.
• As the body’s main vehicle for transporting fats to cells, triglycerides are
important for good health, though high levels of triglycerides can be
unhealthy
In general, the lower your LDL and the higher your HDL, the better your chances of
preventing heart disease and other chronic conditions.

25. How Fat Moves from Food to the Bloodstream

26. How Fat and Cholesterol in Food Affect Blood Cholesterol Levels
• The types of fat in the diet help determine the amount of total, HDL, and LDL
cholesterol in the bloodstream.
• The types and amount of carbohydrate in the diet also play a role. Cholesterol
in food matters, too, but not nearly as much.
• The discovery half a century ago that high blood cholesterol levels were strongly
associated with an increased risk for heart disease triggered numerous warnings
to avoid foods that contain cholesterol, especially eggs and liver.
• However, scientific studies show a weak relationship between the amount of
cholesterol a person consumes and his or her blood cholesterol levels

27. How Fat and Cholesterol in Food Affect Blood Cholesterol Levels
• In studies of more than 80,000 female nurses, Harvard researchers found that
consuming about an egg a day was not associated with higher risk of heart
disease.
• However, people who have heart disease or diabetes should monitor egg
consumption

28. Functions of fat in the diet
1. It is a concentrated source of energy, yielding more than twice the energy
supplied by carbohydrate per unit weight
2. Fats are essential for the absorption of vitamins A, D, E, K and especially
carotenoids
3. Some animal fats contain vitamin A and many vegetable fats contain vitamin E
and red palm oil is a good source of carotene
4. Fats contain essential fatty acids (E.g.: linoleic, linolenic and arachidonic acids)
5. Fats helps to reduce the bulk of the diet as starchy foods absorbs lot of water
during cooking

29. Functions of fat in the diet
6. Fats improve palatability of the diet and give satiety value
7. Fats are essential for the utilization of galactose present in lactose
8. Phosphatides an other complex lipids are essential constituents of nervous
tissue
9. Fats are deposited in the adipose tissue and this deposit serves as a reserve
source of energy during starvation
10. Adipose tissue function like an insulating material against cold and physical
injury

30. Findingfoodwithhealthyfat

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DHA And
Eye

32. DHA accumulation in the retina
• choriocapillaries supply the nutrients to the retinal pigment epithelial (RPE)
cells, which delivers them to the interphotoreceptor matrix.
• Low density lipoprotein (LDL) is the main carrier of DHA, and since the RPE cells
contain LDL receptors
• it is likely that the uptake and delivery of DHA to the photoreceptor cells are
receptor mediated with subsequent release of DHA phospholipids, or free DHA,
into the interphotoreceptor matrix.
• Fatty acid-binding proteins (FABPs) present in the interphotoreceptor matrix
bind DHA, and are believed to be involved in the transport of DHA to the
photoreceptor cells.

33. DHAaccumulationintheretina
choriocapilla
ries supply
retinal
pigment
epithelial
interphotore
ceptor
matrix
photorecept
or cells

34. Retinal
Pigment
Epithelium
• RPE is a single layer of hexagonal pigmented cells located in
the outmost part of the neurosensory retina.
• the supplement of nutrients and oxygen to retina
• the sustainment of visual cycle through metabolizing vit- A
• the absorbing of scattered light to reduce photo-oxidation via
melanosomes
• the performance of receptor-mediated phagocytosis of
photoreceptor outer segment (POS) fragments for assuring
viability and functionality of photoreceptors
• Dysfunction of RPE resulted from consistent exposures to
oxidative stress has been reportedly to cause retinal
degenerations, such as age-related macular degeneration
(AMD).

35. Disc
Shedding
in retina
• The heterophagy of Photoreceptor Outer Segment by RPE is
essential to the longevity of photoreceptors.
• The renewal of POS is regulated by circadian rhythms via the
shedding of distal tips POS, which are degraded and engulfed
by RPE, and are eventually digested by lysosomal enzymes.
• All-trans-retinol (ROL) are recycled and converted to 11-cis-
retinal (11CR) by visual cycle to replenish chromophore for
reproduction of photobleached pigments.

36. Disc
Shedding
in retina

37. DHA conservation in the retina
• Disc membranes are assembled at the inner segment, and form discs at the base
of the outer segment
• These membranes have a short lifetime, and are replaced every 9–14 days
• The discs move outward toward the tip apical region where they are shed into
the adjacent RPE, phagocytosed and digested by the lysosomal system.
• However, the retina conserves its DHA by retrieving it from the phagosomal
membranes within the RPE and recycling it for incorporation into newly forming
disc membranes

38. DHAaccumulationintheretina

39. DHAaccumulationintheretina

40. DHAandeye

41. DHA conservation in the retina
• The recycling mechanism is not fully understood, but it has been postulated to
occur via one of the two following mechanisms:
• (1) by returning the DHA from the RPE back to the photoreceptors (short-loop)
• (2) by entry of DHA into the systemic circulation, where it follows a similar
pathway to cellular and dietary DHA via the liver, and reuptake by the RPE cells,
with delivery to photoreceptor cells for new disc formation (long-loop)
• This selective retention of lipid is unique to the photoreceptor cells.

42. Role of DHA
1. DHA affects the membrane structure by altering its permeability, fluidity,
thickness and lipid-phase properties while increasing the rate of rhodopsin
activation
2. DHA surrounds rhodopsin (approximately 60 molecules of phospholipid for
each rhodopsin), excluding cholesterol from creating a fluid microenvironment
within the rod outer-segment membranes
3. membrane fluidity is an important biophysical factor of the disc membranes,
and this fluidity is brought about by the presence of DHA and other PUFAs on
the constituent phospholipids

43. Role of DHA
4. The membrane’s fluid state allows Brownian movement of the protein
components within the plane of the disc membrane, enabling transduction
and amplification of the signal
5. membranes containing DHA have higher MII formation, MII–transducing
interaction and activation and, finally, PDE activation.

44. DHA and retinal oxidative stress
• DHA has high degree of unsaturation
• It is susceptible to oxidation within the photoreceptor disc membranes
• the membrane stabilising substances, vitamin E and taurine, along with the
retinal antioxidants, vitamin C, carotenoids, superoxide dismutase and
glutathione (and its associated enzymes) helps in fighting against oxidative
damage of eye
• However a constant cellular and dietary supply is required to maintain the disc
membranes.
• studies have demonstrated that depletion of DHA from the developing retina
leads to abnormalities in electroretinogram (ERG) and visual evoked
potential (VEP), resulting in reduced visual function

45. Dietary deficiency of DHA and visual function
• diets low in Omega-3 fatty acids led to impaired visual acuity
• The retinal dysfunction occurs due to inadequate disc membrane DHA
phospholipids to support rhodopsin in light capture, and hence MII formation
• Cells compensate this lack of DHA by converting omega-6 EFA linoleic acid to
decosapentanoic acid, which is not efficient in supporting rhodopsin.
• The retinal abnormalities due to DHA deficiency are reversible
• but the responsiveness of the visual cortex, and the higher cortical centres
involved in visual function, appear long-lasting and irreversible
• In infants: supplementation should be approached with caution as these
infants have low retinal levels of vitamin E and increased retinal DHA
concentration could increase susceptibility to retinal oxidative damage